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The Audiogram
When your child has a hearing test, the test results will be displayed on a graph called an audiogram (see above). This graph will show the softest sound levels each ear can hear sounds of different pitch.
The softness or loudness of the sounds presented are graphed from top to bottom. This is measured in deciBels hearing level (dBHL). If your child responds to sounds at very soft levels, the marks will be closer to the top of the graph. If there is hearing loss, the marks will be made further down on the graph. The further down the marks are, the more hearing loss there is. The American Speech-Language Hearing Association (ASHA) defines the different levels of hearing loss as follows:
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Normal hearing: -10dBHL to 25dBHL
Mild hearing loss: 26 dBHL to 40 dBHL.
Moderate hearing loss: 41 dBHL to 55 dBHL.
Moderately severe hearing loss: 56 dBHL to 70 dBHL
Severe hearing loss: 71 dBHL to 90 dBHL
Profound hearing loss: 91dBHL +
From left to right on the graph are the different frequencies or pitches that are tested. This is measured in Hertz (Hz). Think of frequencies like musical notes. They are graphed from low pitch to high pitch from left to right on the graph, just like the keys are set up on a piano.
Low frequency hearing loss: 250 Hz to 1000 Hz.
Mid-frequency hearing loss: 1000 Hz to 4000 Hz.
High frequency hearing loss: 4000 Hz to 16000 Hz.
ASHA also discusses other terms you may hear when discussing an audiogram:
Unilateral/bilateral: One ear/both ears have hearing loss
Symmetrical/Asymmetrical: The ears hear the same/the ears hear differently
Progressive hearing loss: The hearing loss is getting worse
Fluctuating hearing loss: The hearing loss can be better and worse at different times
Sudden hearing loss: The hearing loss happened very quickly
Reading the audiogram
When you first see an audiogram, you will notice many colors and symbols on the graph. Each of these marks is important. Every audiogram should have a key on the page to help you understand what you are seeing.
If your child was tested in soundfield, these responses are written on the audiogram as an S (for soundfield) or NB (for responses to narrow band noise).
Responses for air conduction (AC) hearing (when your child wears earphones) and bone conduction (BC) hearing (when your child wears a bone conduction vibrator) are shown on the graph. Remember that air conduction tests the outer, middle, inner and neural parts of the ear. Bone conduction tests only the inner and neural parts of the ear.
Here’s an audiogram showing hearing for the right and left ears.
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The right ear’s responses are shown in red.
AC responses: circles
BC responses: a “greater than” sign
The left ear’s responses are shown in blue.
AC responses: X
BC responses: a “less than” sign
Masking
If the ears hear very differently from each other, or if there is a conductive/mixed hearing loss, the audiologist will use a technique known as masking. Because the inner ear is actually part of the skull, if you make a sound loud enough, both cochleas will actually respond to the sound, making it hard to tell which ear hears what.
Masking will be used when:
air conduction testing shows a difference of 40dB or more between the hearing levels in each ear at each frequency
bone conduction testing shows a 10 dB or more difference between air and bone conduction levels in each ear at each frequency
To use masking, the audiologist will initiate a noise in the better hearing ear that sounds like static. This will keep the better ear busy listening to the noise, ensuring that only the poorer ear will be responding to the tones. If masking is used, there are different symbols to show this on the audiogram.
Right ear will be shown in red
Masked AC: triangle
Masked BC: [
Left ear will be shown in blue
Masked AC: box
Masked BC: ]
Here is an audiogram showing that masking was used to test the left ear, since it is worse-hearing than the right ear.
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The loudness limits of an audiometer are not without a ceiling. If your child has a very severe hearing loss, you may see marks made at the very bottom of the graph with downward arrows coming from them. these marks indicate that hearing loss is so severe that the audiometer was not able to produce a sound loud enough for your child to hear. Here below is an audiogram depicting these symbols in the mid to high frequencies in both ears.
Photo credit http://www.raisingdeafkids.org
First Steps 